Place a wire rack over a burner on the stove. Roast the poblanos on the rack and turn with tongs until blackened evenly. Remove from heat and set aside.
Heat canola oil in a medium heavy nonstick saute pan over medium heat. Add the onion and zucchini and saute until golden, about 5 minutes. Add the cumin, oregano, garlic powder, tomatoes, green chiles and corn. Continue to cook until the mixture is almost dry.
Meanwhile, use a paper towel to rub off the skins from the poblanos. Make an incision on 1 side, and remove seeds and membranes from inside, while making sure to keep the poblano intact.
Heat a medium heavy nonstick saute pan over medium heat. Lightly spray with canola cooking spray for 2 seconds. Evenly stuff the 4 poblanos with the zucchini mixture and the shredded cheese.
Carefully place the stuffed poblanos in the heated saute pan and sear on each side for approximately 2 minutes, or until golden brown. Serve warm with tomato salsa.