Season steaks liberally with salt and pepper and grill to rare.

In skillet over medium-high heat, melt butter and onions. Season with salt and pepper. Cook stirring frequently until light brown. Remove from heat.

Thinly slice steaks and cut into thirds. Mix steak with onions and warm for a few minutes.

Arrange layer of TOSTITOS^® on oven-proof platter. Top with salsa, half of steak mixture, and half of cheeses. Repeat with additional layer. Place platter in 400° oven for 3-5 minutes to melt cheese.

Top with TOSTITOS^® Avocado Salsa Dip and serve.