Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a small to medium dry pot, toast the cumin and coriander seeds over medium heat, stirring, until fragrant, about 1–2 minutes; transfer to a spice grinder and grind to a powder.
Remove stems and seeds from the poblanos and fresh chili and cut into roughly 2-inch pieces; place them on the prepared baking sheet.
Add the sliced onion, halved tomatoes, and peeled garlic cloves to the baking sheet; toss vegetables with the ground cumin and coriander, avocado oil, and salt and pepper to taste.
Roast the vegetables in the oven for about 20 minutes, until lightly browned and softened; let cool slightly.
Transfer the roasted vegetables to a blender or food processor and pulse a few times until you have a chunky paste with no large pieces of garlic or chili; scrape the mixture into the pot used earlier.
Add the rinsed brown basmati rice, drained black beans, tomato paste, coconut aminos (or tamari), and 2 1/4 cups filtered water to the pot with the puréed vegetables; stir to combine.
Bring the pot to a boil over medium heat, then reduce to a simmer and cover; cook gently for about 40 minutes, stirring and checking every 10–15 minutes, until the rice is tender and most liquid is absorbed (add a splash more water if needed).
Remove the pot from heat and let rest, covered, for 5 minutes. Uncover and stir in the lime juice, chopped cilantro, and an extra pinch of salt if desired.
Serve the black beans and rice hot.