Start by making the rice. Place rice in a small saucepan with 2 cups of water. Bring water to boil, cover, and reduce heat to a simmer. Simmer for 45 minutes or until all the water has absorbed. Note: If you are making white rice this should only take 20-25 minutes.
Combine 2 tablespoons of olive oil and the remaining ingredients for the portobello steak marinade. Clean and chop the portobello into 3/4" slices. Place them in a large plastic zip bag. Add the marinade and toss together until the portobellos are fully coated. Place in the refrigerator while preparing the rest of your ingredients.
Heat up the beans and prepare the guacamole if making from scratch.
Slice the onions and peppers. Heat one tablespoon of olive oil in a large skillet over medium-high heat. Once hot, reduce heat to medium and add onions and peppers. Sauté for 5-10 minutes until the edges have begun to char. Remove from heat.
Wipe the skillet clean. Add an additional tablespoon of olive oil. Add portobello strips and any reserved marinade to the hot skillet and cook over medium-high heat for about 8 minutes, flipping once, until the mushrooms have decreased in size and are charred on both sides.
When the rice is done, toss it with lime juice and cilantro.
To assemble the bowls, place a scoop of rice on the bottom of each bowl. Top with portobellos, fajita vegetables, and both kinds of salsa. Add guacamole, corn, beans, and fresh lime wedges and serve.