You can use what ever type of beans and squash you like or have on hand, it's pretty versatile.
Begin with your chiles. (You can also use peppers if you wish!) You can slice in half lengthwise to fill, or cut off the stem end to fill. I go the stem end route.
After you have your chiles/peppers ready to go, lightly saute about a half-cup of diced onions in 2 tablespoons of butter. (Seems like a lot, but it won't be later...)
While you do that, dice your squash. You'll want it at about 1/4 inch. We used zucchini here, because that's what looked good at the grocer this week. It was a medium sized squash that gave us about a cup diced.
When your onion is ready, turn off the heat, add your squash and stir. It will use up the rest of the butter and sliiiiiightly cook.
In a bowl, combine one cup of frozen or fresh corn, and a cup and a half of beans. (Canned or home-cooked...) We used black beans here. Mix in your onion/zucchini mixture. Add to that a tablespoon of lime juice, a teaspoon of cumin, and salt to taste. I also added a half-cup of shredded cheese to help slightly bind it. This will still be a very loose stuffing.
Begin stuffing into your chiles/peppers. If you are using the chiles and stuffing from the top, make the first couple spoonfuls very loose, and kind of wiggle the goodies down to the pointed end. If halved, you'll just need to spoon it on. Arrange in a pan and preheat your oven to 400.
Bake for about 20-25 minutes, sprinkle with more cheese if desired, and let it go another 15 minutes or so.
We like to serve them with tortillas to help get the lose filling and cheesiness to our mouths.