Season the chicken breast evenly on both sides with sea salt, black pepper, garlic powder, and ground cumin.
Place a large skillet over medium-high heat and add the whole jalapeño, dry-searing it until the skin is blistered and charred on all sides.
Remove the jalapeño from the pan, slice it into rounds (removing seeds if less heat is desired), and set aside.
Add the olive oil to the same skillet, then place the chicken breast in the pan and cook for 6-7 minutes per side until golden brown and the internal temperature reaches 165°F.
While the chicken cooks, mash the avocado in a small bowl with a splash of lime juice and a pinch of salt.
Remove the chicken from the pan to rest, then add the sliced bell peppers and red onions to the skillet, sautéing for 3-4 minutes until tender-crisp.
Slice the chicken into strips and assemble your bowl by layering the cooked brown rice, sautéed vegetables, sliced chicken, and charred jalapeño.
Top with the avocado mash and a final squeeze of fresh lime juice before serving.