As a note, I make pulled pork a multitude of different ways: in the crockpot, in the oven or even on the stovetop (this is the ONLY way my mom makes it). You can use whatever pork you have on hand for this recipe!
To make the tortillas, heat a large skillet over medium heat and add olive oil and butter. Add each tortilla and cook until golden and crisp on both sides, about 2 minutes per side. Remove the tortillas and set them on a paper towel to drain any excess oil and cool and crisp up slightly.
In a bowl, toss the tomatoes, cilantro, onion, lime juice, salt and pepper. Assemble the tostadas by placing some pork on the tortilla, then covering it with cheese, shredded lettuce and the tomato mixture. Add a little more cheese on top. Serve!