Place the cooked spaghetti squash in a bowl. Sprinkle the chili powder and a pinch of salt over the spaghetti squash. Toss the spaghetti squash in the seasoning until evenly covered. Taste and adjust the salt if needed.
Drain the black beans, shred the cheese, and slice the green onions. Divide the spaghetti squash between four bowls, then add 1/3 cup beans and 1/4 cup salsa to each bowl. Top each bowl with shredded cheese and a few sliced green onions. Refrigerate until ready to eat. Reheat in the microwave just before serving (one minute on high, stir, then add more time in 30 second intervals until heated through).