Lay fish in a baking dish and pour lemon juice, salt, and pepper on top. Let sit while you prepare the sauce.
In a large pan, heat a tablespoon of olive oil. Add garlic and jalapeño and cook for 2-3 minutes. Add in tomato paste, water, and remaining oil. Bring to a simmer and let reduce slightly.
Add cilantro and stir. Add fish, skin side down, and the lemon juice from the pan. Spoon a little sauce on top. Cover and cook over medium heat for 18-20 minutes.
Meanwhile, heat a little olive oil in a separate pan. Add Brussels sprouts, cut side down, and cook over medium heat for 10-12 minutes, until soft. Add salt to taste.
Serve both Brussels sprouts and fish with the spicy sauce on top.
Recipe by Things I Made Today at https://www.thingsimadetoday.com/2013/10/01/tunisian-fish-stew-brussel-sprouts-plus-new-kitchen/