In a small bowl, add 1/4 cup of the canola oil, the cumin, 2 teaspoons chili powder, and season with salt and black pepper, to taste. Stir to combine. Brush each ear of corn liberally with the seasoned oil.
Arrange the corn on the hot grill and cook for about 12 minutes, giving each ear a quarter turn every 3 minutes. Remove from grill and let cool for 5 minutes. When cool enough to handle cut kernels from corn.
In a medium serving bowl, whisk together the remaining 1/4 cup of canola oil, 1 teaspoon chili powder, the lime juice, garlic, bell pepper, onions, beans, and cilantro. Adjust the seasonings with salt and black pepper, to taste. Add the corn kernels and stir to combine. Mix the ingredients well and serve with tacos, if desired.