Preheat the oven to 400 F, prepare a small pan or muffin pan, and line a baking sheet with parchment paper.
Peel and discard the papery outer layers of the whole garlic bulb. Use a sharp knife, cut ¼ to ½ inch from the top of the garlic head. Drizzle with 1 teaspoon of oil, rub it around, then cover the garlic with foil. Place it in the pan or muffin pan (to keep it from rolling), cut side up.
Spread out the cherry tomatoes and sliced onion in a single layer on the baking sheet. Drizzle with 2 teaspoons of olive oil and sprinkle with oregano, salt, and pepper.
Place both baking pans into the oven for 30 minutes, or until the garlic cloves are lightly browned and the tomato/onion mixture slightly shriveled.
While the garlic and tomatoes bake, start the lentils. In a medium saucepan, bring the broth to a boil. Add lentils and reduce heat. Let it simmer and cover for 25 to 30 minutes. Drain the lentils and transfer to a medium-sized bowl.
Allow the garlic to cool completely, then use a small knife to cut the skin slightly around each clove. Use a fork or your fingers to pull or squeeze the roasted garlic cloves out of their skins. Then mash the garlic with the fork.
Add the mashed garlic, tomatoes and red onion mixture, green pepper, and red pepper to the bowl with the lentils.
For the dressing, combine the olive oil, lemon juice, and crushed pepper in a small bowl. Whisk in salt and pepper. Toss with lentil mixture, sprinkle parsley and/or arugula on top, then serve.