This recipe requires a cast iron skillet, or a ceramic frying pan. I do not recommend the use of teflon-based non-stick cookware for this recipe, because the high temperatures in the oven can ruin the non-stick coating, and evidence suggests that heating teflon can create toxic gases.
Begin by preheating the oven to 350 degrees.
Put your cast iron frying pan on the stove, add the olive oil, and turn the burner to medium-high heat.
Dice the garlic, chili pepper, and red onion, and add to the frying pan. This mixture should get transparent and lightly caramelized, but must not be allowed to burn.
Chop the zuchini into thin rounds, and add to the frying pan.
Cut the chard across the leaf, into quarter-inch wide strips, including the stem. When the zuchini is soft, but not quite cooked through, add the chard to the frying pan. Stir this mixture, to let the chard cook on all sides. It will shrink as it cooks. Add the salt.
Now beat the eggs lightly together, and pour evenly over the top of the vegetable mixture. Don't stir the eggs with the vegetables. Let this cook on the stovetop for five more minutes.
Sprinkle the cheese on top. Move the frying pan to the oven, and cook ten minutes.
Remove the frittata from the oven, and rest for five minutes before cutting into wedges and serving.