Set up your work station with a large baking sheet and 8 metal or wooden skewers. If you’re using wooden skewers and you’re grilling outside, soak them in cold water for at least 30 minutes before cooking. Heat a grill to medium-high heat.
Gently pat the salmon as dry as possible with paper towels. Thread a piece of salmon, a folded slice of lemon, a cube of bell pepper and a cube of onion on one skewer, ensuring that there is about ¼-inch of space between each ingredient. Continue threading the ingredients, alternating each time, until you are about 1-inch from the end of the skewer. Set the finished skewer on the baking sheet. Repeat with the remaining skewers and ingredients.
In a small bowl, whisk together the lemon juice, oil, garlic, oregano, cumin, salt and black pepper. Brush the skewers with the dressing, using all of it.
Grill the skewers until the salmon is opaque and cooked through and the veggies are tender, 3 to 4 minutes per side. I prefer to cover the grill so the salmon has a chance to cook through. Transfer the skewers to a large platter and enjoy.