In a large heavy-bottomed skillet or sauté pan with a lid over medium-high heat, warm 2 tablespoons of the olive oil. Add the garlic and cook until fragrant and just starting to brown, approximately 3 minutes.
Add the tomatoes to the pan and lower the heat to medium-low. Sauté for 3 minutes until the tomatoes release their juices and start to soften.
Add the potatoes to the tomatoes and layer the bell peppers and jalapeños on top of the potatoes. Add the remaining olive on top of the peppers. Cook until everything begins to soften, approximately 4 minutes.
Stir in the cumin, paprika, salt, pepper, and cayenne. Turn the heat down to a very low simmer.
Cover the pan and cook for approximately 1 hour, stirring a couple of times.
Nestle the salmon portions, flat side down, into the sauce, cover the pan, and continue to cook for 10 minutes.
Layer the lemon slices on top of the salmon, cover, and cook for an additional 5 minutes or until the salmon is just opaque.
Serve the salmon with couscous or cauliflower rice. Spoon some sauce with potatoes around the salmon and serve chermoula on the side.