1. Preheat oven to 400 degrees. In a large saucepan, heat 1 tablespoon oil over medium; add white part of scallions and garlic. Season with salt and pepper. Cook until softened, stirring constantly, 2 to 3 minutes. Add beans, tomatoes with juice, and 1/2 cup water. As you bring to a boil, mash about 1/4 of the beans with the back of a spoon against side of pan to release starch. Reduce to a simmer; cook until mixture has thickened, 10 to 15 minutes.

2. Meanwhile, brush eight 10- to 12-ounce ramekins or custard cups with remaining oil. Slice polenta crosswise into 8 rounds; place 1 round in each ramekin.

3. Remove bean mixture from heat. Stir in green part of scallions, cilantro, and hot sauce; season with salt and pepper. Spoon bean mixture into ramekins; top each with cheese. Bake at 400 degrees for 15 to 20 minutes. Let stand 10 minutes before serving. If desired, garnish with cilantro, and serve with salsa.