Cook Skirt Steak: Combine chipotle paste, 1/2 teaspoon Mexican chili powder, oregano, 1 teaspoon salt, cayenne pepper and mayonnaise and mix well. Rub the steak with the mixture; let stand at room temperature for 30 minutes and up to overnight covered in the refrigerator.
Preheat a grill or grill pan over medium-high heat and rub grill or pan with olive oil. When hot, add the skirt steak and cook for 2 to 3 minutes per side or until caramelized and barely pink in the middle. Transfer to a platter to keep warm.
Make Salsa: Combine the tomato, avocado, lime juice, cilantro, the remaining 1/2 teaspoon of Mexican chili powder and the remaining 1/2 teaspoon of salt and mix well; set aside.
Make Tequila Cilantro Sauce: Combine mayonnaise, sour cream, cilantro, tequila, lime juice, salt and cayenne pepper in a small bowl and whisk until smooth.
Heat the refried beans in a small saucepan over medium-low heat.
Assemble Tostadas: Layer each tostada shell with refried beans, skirt steak, shredded lettuce, Avocado Salsa and cheese. Drizzle Tequila Cilantro Sauce on top and serve.