Preheat an outdoor grill (preferably charcoal) for high heat and lightly oil the grate.
Place bacon in a skillet over medium heat and cook until browned and crisp, 8 to 10 minutes.
Cut kernels from corn ears into a large bowl using a sharp knife held at a 45-degree angle. Scrape cobs with the back of the knife into the bowl to get the juices.
Stir white and light green parts of green onions into bacon and add red bell pepper; cook and stir until vegetables just start to become tender, about 2 minutes. Stir corn into bacon mixture and let corn just warm through. Season with salt, black pepper, cayenne pepper, a few chopped dark green onion tops, olive oil, and rice vinegar. Turn off heat under relish.
Spread vegetable oil onto both sides of salmon fillets and season fish with salt, black pepper, and cayenne pepper.
Cook on preheated grill until fish shows good grill marks, the flesh flakes easily, and fish is still slightly pink in the center, about 5 minutes per side. A crack that opens up in the salmon flesh as you cook will let you see how done the salmon is in the middle.
Divide spinach leaves onto 2 plates and top each with a salmon fillet and half the bacon relish. Sprinkle on a few green onion tops for garnish.