What would I suggest a beginner start out with in Ka'u, Hawaii? (Every region is different, so I can only make suggestions for my own immediate area.) I'll go into more detail with each individual veggie in future posts.
Green beans. Just about everyone can be successful with beans. They are easy to germinate. Don't require a lot of space or care. And you get to eat your success in less than two months. Bush beans are easiest to start with unless you already have trellises in place.
Peas. This is another easy, quick crop. Not quite a carefree as bush beans, but not bad. Bush varieties produce quickly and don't need elaborate trellises.
Radishes. Though adequate fertilizer and moisture are required, this crop is easy to grow and ready to start eating in three weeks. Not too many beginners can fail with this one as long as you keep the ground moist.
Leaf lettuce. Another quick and easy crop as long as you provide steady moisture and fertilizer, plus keep the roots cool. The goal is to keep it growing quickly so that you avoid bitterness. Not as easy as the other veggies I've already mentioned, but it's not too difficult.
Chard. If you can grow radishes, you can grow chard. The chard family includes beets, though beets requires a bit more attention than chard.
Bok choy. If you've had success with chards then try bok choy. It's easy and quick.
Once you've had success with these, you can consider graduating to the next level. Still easy to grow, these just need a bit more attention. Failures are more common......
Onions. Keeping it weed free and growing quickly is a bit more challenging. But it can be eaten before it bulbs, so grow plenty and eat it freely.
Kale. When you first try this, you'll say it's simple. But then the diseases and pests show up and you'll discover that it's a little harder to grow.
Tomatoes -- cherry/grape. Fairly easy. Some failures will be due to weather, other to pests and diseases. Soil nutrients are important as is controlling root knot nematode. But the grape types are generally easy to grow as are their cousins, the wild type volunteers.
Turnips/rutabagas. Fairly easy. Soil moisture and fertilizer is important. Pests can be a problem.
Broccoli and collards. As long as you can master the use of dipel, you'll be able to grow these. Adequate soil moisture and fertilizer is important for lush growth, thus mild flavor. More difficult will be another member of this family, cauliflower.
Potatoes. I find these to be incredibly easy, but others don't. Keeping the soil evenly moist is important. Keeping the developing tubers away from the sunlight is important. So if one uses a thick mulch, potatoes aren't difficult.
Sweet Potatoes. Another crop I find to be super easy but that others have difficulty with. They don't require lots of water, in fact prefer it drier. Maybe that's the trick, good drainage and keeping it on the dry side.
Next thing to try might be corn. Adequate water and fertilizer is needed for good sweet corn, and if you don't mind picking off a few ear worms, you should be able to produce corn. Most failures are because a gardener doesn't plant a large enough block of it. Corn relies upon wind pollination, so unless you hand pollinate, corn needs plenty of more corn plants around it.
The following are difficult due to diseases, pests, especially fruit fly and pickleworm.....
Cucumbers. A challenge.
Squashes. A challenge too.
Pumpkins. Just as difficult as their kissing cousins, the squashes.
Slicing tomatoes. Fruit flies are such a nightmare that they make the aphid infestation look like nothing.
Peppers. Not only the pests will get these, but most peppers varieties are very demanding of soil conditions, nutrients, weather.
The really difficult crops will be the melons, especially cantaloupe and honeydew types. Disease usually causes these to fail. Even if you douse melons with commercial chemicals, you will find them a challenge to grow in this part of Hawaii. Watermelons are the easiest member of this family to grow. The first couple months growing them are the easiest...until the pests find them.
Grapes are for the master food grower here in Hawaii. They are susceptible to all sorts of diseases and pests. Commercial grapes are heavily doused with various commercial chemicals, fertilizers, and growth hormones. Learning when and how to use additives will be quite challenging.