Bring chicken broth to a boil in a large saucepan. Add 2 tablespoons butter and salt; stir in brown rice. Cover pot. Reduce heat to low. Simmer until rice is tender, about 45 minutes.
Melt the remaining 1 tablespoon butter in a separate saucepan over medium-high heat. Saute red bell pepper until semi-soft, about 5 minutes. Add onion; saute until soft and translucent, about 5 minutes. Stir in black beans, garlic, cumin, and pepper; cook and stir until fragrant, about 2 minutes. Remove from heat.
Pour vegetables into a large serving bowl; add the cooked rice and toss.