Preheat the oven to 300F
In a large (12”) cast-iron or oven-proof skillet over medium heat, warm the olive oil. Add the onion, bell pepper, and ½ teaspoon salt. Cook for 5-7 minutes, or until the onion and bell pepper have softened, stirring occasionally.
Meanwhile, add eggs and ¼ teaspoon salt to a large bowl and whisk thoroughly until totally smooth (give it some muscle, you don’t want any egg white streaks in there - it should be uniform and a little bubbly when it’s done). Stir in ½ cup of the cheese. Set aside.
In the skillet, add half of the chard and remaining ½ teaspoon salt and cook, stirring occasionally, until the chard wilts down enough to make room for the rest (this should happen in a minute or less). Add the rest of the chard and continue to cook until wilted and tender, about 5 minutes, stirring often. Turn off the heat. Spread the veggies out evenly.
Give the eggs one more whisk, then pour into the pan, distributing it all around. Use a wooden spoon or spatula to evenly distribute the veggies in the frittata. Sprinkle the remaining ½ cup cheese over top.
Transfer to the oven and bake for 20 minutes, or until the eggs are mostly set and no longer jiggly in the center. Let the frittata rest for 10 minutes to finish cooking through and cool off.
Use a knife to loosen the edges. The first slice is always tricky to get out. Slice it up and serve warm with a side of buttered toast or this week’s salad!