Preheat the oven to 400 degrees F (200 degrees C). Place sweet potatoes on a cooking sheet and spread evenly.
Roast sweet potatoes in the preheated oven until tender, 15 to 20 minutes. Set aside and let cool.
Meanwhile, slice 1/2 of the yellow onion and set aside; chop remaining half.
Heat 1 tablespoon grapeseed oil in a pot over medium-high heat. Add chopped onions and cook for 2 to 3 minutes. Add beans and 1/2 taco seasoning packet and mix well. Add fire-roasted tomatoes, reduce heat to low, and simmer beans for 15 minutes.
At the same time, heat remaining grapeseed oil in a skillet over medium heat. Add sliced yellow onions, poblano, and red bell pepper. Mix well and add remaining taco seasoning packet; stir to combine the flavor. Cook mixture for 5 to 7 minutes.
Add cooked rice to a bowl, then add the roasted sweet potatoes, black bean mixture, and sautéed onions, poblano, and red bell peppers.