Cook the red lentils (If you already have leftover cooked lentils prepared, skip to step 2) following the directions here.
Meanwhile, heat up the 1 tablespoon of oil in a saucepan or skillet on medium heat. Once the oil is hot, sauté the onions in the oil for a minute, then add the mushrooms and cook for about 5 minutes.
When the lentils are cooked, drain and measure out 2 cups of cooked lentils. Add the seasonings (cumin, garlic powder, salt and pepper) to this drained amount. Stir to mix in the seasonings.
Using a wooden spatula, move the chopped mushrooms and onions mixture to the side of the saucepan and pour the remaining half tablespoon of oil on the empty side of the saucepan. Add the minced garlic and sauté for about 1-2 minutes or until the garlic turns golden.
Add the chopped tomatoes and the dried or fresh basil to the garlic and stir quickly, cooking for 1-2 minutes until the tomato pieces soften.
Add the seasoned cooked lentils to the tomato mixture, and stir to combine. Cook for another 2-3 minutes to heat up the lentils.
Combine the lentil tomato mixture with the mushrooms and onions. Stir all together. Once heated through, add the chopped spinach leaves (optional). Stir and cook for another 2 minutes until the spinach leaves are just wilted. Taste and adjust seasonings (you may add a bit more salt and pepper if you desire!). Serve warm.