Turkey Burgers With Cajun Grilled Onions

Name: Turkey Burgers With Cajun Grilled Onions
Ingredients: 1 1/4 pounds ground turkey (dark meat or 93 percent lean or less); 3/4 cup grated Gruyère or Swiss cheese (3 ounces); 2 cloves garlic, finely chopped; 1/2 teaspoon chili powder; kosher salt and black pepper; 1 large onion, sliced into 1/2-inch-thick rounds; 1 tablespoon olive oil; 2 teaspoons Cajun or blackening spice mix; 4 hamburger buns