Place the salmon fillets in a 9x13-inch baking dish or shallow dish. Add 3 tablespoons of olive oil, the balsamic vinegar, smoked paprika, chopped oregano, chopped shallot, minced garlic, and a pinch each of crushed red pepper flakes, kosher salt, and black pepper. Rub the mixture evenly over the salmon and toss the lemon slices into the oil.
Make the orzo salad: in a large serving bowl combine the cooked orzo, 1/3 cup olive oil, juice of 1 lemon, 1 cup chopped herbs (basil/dill/chives), and a pinch each of crushed red pepper flakes, salt, and pepper.
Add the chickpeas, chopped roasted red pepper, halved cherry tomatoes, green olives, diced cucumber, and diced avocado to the orzo. Toss gently to combine.
Preheat a grill, grill pan, or skillet to medium-high heat. Place the salmon skin-side down and add the lemon slices from the marinade to the grill alongside the fish. Cover and cook 4–5 minutes, then flip the salmon and lemons and cook another 3–4 minutes, until the salmon is opaque and cooked through.
Chop the grilled lemon slices finely and mix them with the remaining 3 tablespoons olive oil, 8 ounces crumbled feta, and 1/2 cup chopped herbs to make the lemon feta topping.
Stir a couple spoonfuls of the lemon feta into the orzo salad to taste. Divide the salad among plates, top each with a salmon fillet, and spoon the remaining lemon feta over the salmon. Garnish with extra fresh herbs and an optional squeeze of lemon.