Get water boiling in a steamer pot. Cut the bell peppers in half length-wise and remove the seeds and membranes. Place peppers in steamer basket and steam for about 3 minutes. You don't want to cook them to be soft, just enough to get a head start so you don't have to bake them as long. Remove to clean towels and let cool as you prepare the filling.
Add olive oil to a skillet and saute onions, garlic, serrano and sweet potatoes until just tender, about 5 minutes. Place in a bowl to cool slightly.
Add cooked rice and beans, corn and spices to the vegetable saute and mix well.
Place half of the Tomato and Red Chile sauce (above) in the bottom of a glass baking dish. Generously stuff the pepper halves with filling mixture and place in the dish. Then drizzle the remaining tomato and red chile sauce over peppers. Sprinkle cotija cheese over the peppers, if using, cover with foil and bake in the 350 degree oven for about 30 minutes. If you like, you can remove the cover and broil for a few minutes at the end to make the tops bubbly, but I didn't do that!
While peppers are baking, make the Vegan Cream Sauce (below)
Serve drizzled with Vegan Cream Sauce and cilantro leaves.