Boil the lentils in salted water for 16-18 minutes until tender, but not mushy. Then drain and rinse well. Allow them to sit in a colander for about 15 minutes to ensure all the water has drained off, or pat them with a paper towel to remove any excess water. (Or use drained and rinsed canned lentils, or precooked lentils.
Preheat the oven to 375°F (190°C).
Spread the lentils in an even layer on a baking sheet, then drizzle with 3 tablespoons of olive oil and sprinkle with 1/4 teaspoon of garlic powder, 1/4 teaspoon of onion powder, 1/4 teaspoon of cumin, and 1/4 teaspoon of salt.
Bake for 10 minutes, then stir the lentils, shake the pan to even them out, and return to the oven for 10 more minutes. Repeat this step again after 10 more minutes of baking, then place them back in the oven for 5-10 more minutes, depending on the desired level of crispiness.
Notes
Watch the lentils closely towards the end of baking to ensure they don't burn.
Feel free to use any spices that you choose to season the lentils. However, you just want a light coating of seasoning, or the spices can burn during baking.