Adjust the oven rack to the middle position and preheat the oven to 350℉ (178℃). Grease a 10-inch baking pan or muffin pan, and set aside.
Using a sharp knife, cut both ends off the plantain to make it easier to grab the skin. Slit a shallow line down the length of the plantain only as deep as the peel. Remove the peel by pulling it back. Slice the plantains into the desired shape and size.
Place them on the baking sheets in a single layer, spray lightly with canola oil, and bake for 8 minutes. Turn the slices over, and bake for another 5-15 minutes or until golden brown, depending on your oven.
While the plantains are baking, heat a medium saucepan over medium-high heat and add a drizzle of oil. Sauté the onions, tomatoes, and green pepper for 4-5 minutes.
In a large bowl, whisk the eggs, add the sautéed vegetable mixture, and season with salt and pepper to preference. (I put two pinches of salt.)
Pour the egg mixture into the greased 10-inch baking pan. Layer the baked plantains on top and sprinkle with parsley.
Bake for 30-40 minutes, or until the mixture is firm in the center.
Let it cool for a few minutes; top with avocado if desired.