Heat vegetable oil over medium-high heat in a non-stick skillet until shimmering, 2-3 minutes
Cook tortilla squares until they start to turn golden, stirring ocassionally, about 5 minutes
Add diced onions and cook until they begin to soften and become translucent, stirring occassionaly, about 3-4 minutes
Add in the pepper strips, and mix thoroughly, allowing them to heat through, 2-3 minutes
Whip the milk and eggs together in a bowl and add to the pan. Add salt to taste
Reduce the heat to medium-low and stir to incorporate thoroughly. Stir frequently to ensure that the eggs are cooking evenly and no ingredients are sticking to the bottom of the pan.
Just before the eggs are done to your liking, add in the cheese and stir to incorporate. Turn off the heat and allow the cheese to melt slightly.
Serve immediately