Slice each bell pepper in half top to bottom through stem. Remove seeds and membranes. Place in a rectangle 9x13" casserole dish (or two 8x8" to accommodate) that has been sprayed with cooking spray or olive oil. Bake for 25 minutes uncovered.
Heat oil in a large skillet over medium-high heat. Add the onions and season kosher salt. Cook until soft, 3 minutes. Add ground beef to hot skillet, break up with spoon. Drain excess fat if necessary.
Add Taco Seasoning and Salsa Verde and cook until beef has browned and sauce has reduced and thickened. Remove from heat and add to large bowl.
Add the cheddar cheese, pinto beans and cooked rice to seasoned beef in bowl. Stir to incorporate and heat through. Divide and spoon mixture into each baked pepper, reserving any leftover filling for other use or freeze.
Place in oven to bake 10 minutes to melt cheese and heat through. Serve with Pickled Onions and crumbled Queso Fresco or Cotija cheese if desired, or more salsa verde.