Combine 2 cups water, lentils, cumin, garlic powder, and 1 teaspoon salt in a pot over medium heat; bring to a simmer. Reduce heat to low; cook until lentils begin to soften, 20 to 30 minutes.
Stir rice, remaining ¾ cup water, remaining 1 teaspoon salt, and olive oil into lentils. Cover pot; continue cooking until lentils and rice tender, about 40 minutes more.
Heat vegetable oil in a skillet over medium heat. Add onions; cook and stir until browned, 7 to 10 minutes. Top rice and lentil mixture with onions; serve.
