Preheat the oven to 400ºF. Place the sweet potatoes on a sheet pan lined with parchment paper. Place the onions and bell peppers on a second parchment paper lined sheet pan.
In a small bowl, mix the ground cumin and chili powder. Set aside.
Drizzle the sweet potatoes with olive oil and sprinkle with salt, pepper, and 2 ⁄ 3 of the spice mix. Toss to coat evenly.
Next, drizzle the onions and bell peppers with olive oil, sprinkle with salt, pepper, and remaining spice mix.
Place both pans in the preheated oven and bake until the sweet potatoes become tender and the onions and bell peppers are tender and caramelized on the edges, about 30 to 35 minutes, tossing once halfway through.
Place the avocado in a large bowl and smash it with a fork until smooth. Add lime juice and season with salt and pepper to taste. Next add the rice and the chopped cilantro. Gently mix the ingredients until the avocado and cilantro are evenly distributed. Taste and adjust seasoning.
Divide the rice into 6 serving bowls. In the same large bowl where you mixed the rice, place the black beans, corn, jalapenos and lime juice. Season with salt and pepper and toss to combine.
To finish assembling the bowls, top the rice with the roasted sweet potatoes, roasted bell peppers, roasted onions and the black bean and corn mixture. Serve with your desired toppings (optional)