Heat canola oil in a large nonstick skillet over medium-high heat until shimmering. Add the vegetable mixture, pressing gently on the top and sides with a spatula to shape it into a large pancake. Cook until a golden crust forms on the bottom and edges, 6 to 9 minutes. (Reduce heat, if necessary, to prevent burning.) To flip, carefully place a large plate or inverted rimless baking sheet over the pan and quickly invert. Slide the pancake back into the pan, browned-side now facing up. Continue to cook until the vegetables are tender and the bottom is golden, 3 to 4 minutes more.