Preheat the oven to 350 degrees F.
Start by grilling the corn (or using leftover grilled corn from dinner the night before!). Preheat your grill to the highest heat.
To grill the corn, rub the ears with the olive oil. Lately, I’ve been grilling my corn without the husks on, tied at the bottom, and without foil, so it takes only a few minutes. Place the ears on the grill and cook until the corn is golden or charred – whichever you prefer – turning the ears as you go. Remove them from the grill and let them cool. Slice the kernels off the cob.
In a bowl, combine the corn and zucchini. Stir in ⅓ cup of enchilada sauce and ½ cup of grated cheese. Make sure the filling is combined well.
Spray a 9x13 inch baking dish with nonstick spray. Spread ½ cup of enchilada sauce on the bottom of the dish. Take your corn tortillas and add a tablespoon or 2 of filling in each, rolling them up and placing them seam-side down in the dish. Repeat with all the tortillas and filling.
Top the enchiladas with the remaining sauce, using a spoon to spread it over all the tortillas, covering each piece. Add the grated cheese on top.
Bake for 20 to 25 minutes, until golden and bubbly. Top with the cotija cheese, cilantro and pickled onions. Serve immediately!