Preheat oven to 350°. Sauté the onions in the oil for about 8 minutes, until translucent. Stir in the tomatoes, corn, black beans, lime juice, salt & pepper and continue to sauté for8-10 minutes, until heated through.
Meanwhile, in another saucepan, blanch the greens in boiling water until just wilted. Drain & set aside.
Lightly oil an 8x8 casserole dish. Spread half the crushed tortilla chips on the bottom. Spoon the sautéed vegetables over the tortilla chips and sprinkle about 2/3 of the grated cheese on top. Arrange the greens evenly over the cheese and spoon on half the salsa. Add the remaining tortilla chips, then top with the remaining salsa & cheese.
Bake for 35-40 minutes, until the cheese is bubbling & beginning to brown.
Serves 4-6