To make the spice rub: In bowl, mix together all the ingredients.
Rub 2 teaspoons of the mixture into the flesh of the salmon fillet; set aside for 30 minutes. Preheat the oven to 200 F.
In a large cast-iron skillet, cook the bacon over medium heat until crisp and the bottom of the pan is coated with the rendered fat, 5 to 8 minutes. Transfer the bacon to paper towels to drain, then cut into small pieces.
Put the skillet over high heat. When the fat is hot, gently put the salmon in the pan, pinker-side down. (One side of a salmon fillet will be bright pink and the other side will have a strip of dark flesh running down the center. The bright pink side is the one you want to brown.) Sear until nicely browned on the bottom, about 3 minutes. Using two large spatulas, carefully transfer the salmon to a sheet of heavy-duty aluminum foil, browned-side up.
Add the onion to the fat in the pan and sauté over medium-high heat until translucent, about 2 minutes. Add the garlic and the remaining spice blend and stir until aromatic, about 20 seconds. Stir in the lentils, tomatoes with their juice, and broth and simmer for 10 minutes.
Using the foil as a kind of large spatula, carefully slide the salmon onto the lentils. Cover the skillet with a lid or a clean sheet of heavy foil and bake until the thickest part of the fish flakes to gentle pressure and the lentils are tender, about 1 hour.
Garnish with the chopped cilantro and slip onto a large platter or serve directly from the pan.
Variation: In a Slow Cooker
Follow the directions in the recipe. Use a sheet of heavy-duty aluminum foil 2 feet long for resting the browned salmon. Scrape the lentil mixture into a 5- to 6-quart, oval-shaped slow cooker. Using the foil as a plate, set the salmon, still on the foil, on top of the lentils. Drape the long ends of the foil up the sides and over the edges of the slow-cooker crock, like handles. Cover and cook on low for 2 hours. Lift the salmon on its foil sling. Mound the lentils on a serving platter and carefully slide the salmon from the foil onto the bed of lentils. Garnish with the chopped cilantro and serve.