Whisk together eggs and cheese until creamy. Fold in spinach and set aside.
Heat oil over medium heat in an oven-proof skillet. Saute leek, carrot, and cayenne peppers until the leek is translucent, 4 to 5 minutes. Add chickpeas and tomatoes. Saute until warmed through, about 3 minutes. Add egg mixture to the skillet and cover.
Cook the mixture undisturbed until the edges of the frittata have firmed and slightly browned, 4 to 5 minutes. Reduce heat to medium-low. Replace the cover but watch every so often until the whole frittata has firmed except the very middle. Take care to keep the heat source on medium-low to avoid burning bottom of frittata.
Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Place the frittata under the broiler to firm and brown the top, 1 to 3 minutes.
Allow to cool before serving. Top with red pepper flakes if desired.
Serve warm or at room temperature with an ice cold glass of milk!