Steak quesadilla w/ cilantro pesto

INGREDIENTS
-Large tortillas
-Mozzarella
-Flank steak
-2 cups fresh cilantro leaves, packed
-1/2 cup pine nuts, toasted
-3 cloves garlic
-1/2 cup grated Parmesan cheese
-1/2 cup extra-virgin olive oil
-Juice of 1 lime (about 2 tablespoons)
-Salt and freshly ground black pepper to taste