Whisk together lime juice, oil, cumin, and cayenne (if desired) in a medium bowl. Add beans; toss well to coat. Season with salt and pepper. Cover, and refrigerate at least 3 hours or overnight.
Toss together mango, cilantro, scallion, and jalapeno in a medium bowl. Refrigerate, covered, until ready to serve.
Preheat oven to 375 degrees. Have a standard muffin tin ready. Sprinkle 1 tablespoon cheese on a nonstick baking sheet to form a rough 3-inch circle. Make 3 more circles. Bake, rotating sheet after 4 minutes, until circles appear lacy and sizzle in middles, 6 to 7 minutes total.
Using a spatula, immediately transfer 1 circle to a cup in muffin tin; gently push down with fingers to form a cup shape. Repeat with remaining circles. Continue forming and baking cheese circles in batches until all cheese is used. Remove cheese cups from tin when cool.
Just before serving, place 1 heaping tablespoon beans and 1 tablespoon mango salsa in each cheddar cup.
Kimkim, I haven't tried these cups with cheddar yet, but I've made them before with Parmesan using the same method as this and they worked well... perhaps it was because it is a harder, less melt-y cheese? I think I will use parmesan in this recipe when I try it. (sorry about your gooey mess...) I used a rammekin turned upside down as my cup mold. This might be easier to remove after it's cooled?
If anyone has any tips on making the cheese cups please share! Mine just ended up gooey melted cheese on a baking sheet. Not sure what I did wrong.