Heat the olive oil in a large pot over medium heat. Add the onion and cook for 5 minutes until it softens.
Stir in the garlic and cook for 1 minute. Add the harissa paste and stir for another minute to release its aroma.
Add the lentils and vegetable broth. Bring the mixture to a boil, then reduce to a simmer. Cover and cook for 20 minutes.
Stir in the diced tomatoes, chickpeas, roasted red peppers, salt, and black pepper. Simmer uncovered for 15 more minutes until the lentils are tender and the stew thickens slightly.
Remove from heat. Stir in the parsley just before serving. Serve with lemon wedges on the side.