Heat the oil in a skillet over medium-high heat. Add the onion and cook about 5 minutes. Add the garlic, zucchini, yellow squash, oregano, and cumin and continue to cook until vegetables start to brown, about 4 to 5 minutes. Add the corn, sauté for a minute or two and remove from the heat.
Mix the cheeses together. Pour about ½ cup of the enchilada sauce in the bottom of your slow cooker and spread it around. In layers add one-quarter of the tortilla strips, one-quarter of the enchilada sauce, one-third of the veggies, and one-quarter of the cheese blend and then sprinkle with one-quarter of the queso fresco. Repeat the layers, ending with the queso fresco. Your last layers will be tortillas, sauce and cheese (no veggies). Cover and cook on high for 2 hours or low for 4 hours.