I'll go a step further and say that any lettuce (or vegetable-like substance) is the antithesis of Frito Chili Pie.

Layer of Fritos, top with chili and optional diced onions.
Repeat layers.
Top with cheese*
Bake.

That is all.

*Shredded colby or cheddar, at the ballpark it might be nacho cheese sauce, but the best cheese is actually the government-surplus-food-stamp cheese. Thankfully, I don't even know if they make that stuff anymore.