Combine scallops and 2 tablespoons flour in a large zip-top bag; seal bag and shake gently to coat scallops.
Heat oil in a 10-inch cast-iron skillet over high heat, swirling to coat bottom of pan. Add scallops; cook 2 minutes on each side or until lightly browned. Remove scallops from skillet; keep warm.
Melt margarine in skillet over medium heat. Add 2 teaspoons flour, and cook 30 seconds, stirring constantly. Add chili powder, salt, and cumin; cook 30 seconds, stirring frequently. Gradually stir in milk, and cook 2 1/2 minutes or until thick, stirring frequently. Return scallops to skillet; add cilantro, stirring gently to coat. Garnish with cilantro sprigs, if desired.