Peel and slice onions to about 1/8-inch thick — thin enough to cook quickly, thick enough to avoid scorching. Yellow or Spanish onions work best. Limit to 2 large onions per 12-inch Skillet to prevent steaming. Have your fat ready and keep a splash of water, broth, or wine nearby to deglaze if needed.

Heat a Skillet over medium to medium-high heat. Add butter, oil, or a mix and let it shimmer. Add sliced onions in large handfuls, stirring for 1–2 minutes per batch until they begin to soften — this prevents overcrowding. Once all onions are in, season with a pinch of salt. Cook over medium heat, stirring every few minutes, for 8–12 minutes total until soft, translucent, and lightly golden. To speed up softening, add 1/4 to ½ cup water or broth and cover; steam wilts the onions in a few minutes. Remove the lid once liquid evaporates and continue cooking uncovered. If the pan looks dry, deglaze with a splash of water, broth, or wine, scraping up any browned bits. Don't crank the heat — high heat burns the outside before the onions cook through.

Heat the 1 tbsp olive oil in a large Skillet over medium-high heat until shimmering. Place the 4 piece salmon fillets skin-on, about 6 oz each, patted dry skin-side up and cook undisturbed for 4–5 minutes until a golden crust forms. Flip the fillets and cook for another 3–4 minutes on the skin side until the 4 piece salmon fillets skin-on, about 6 oz each, patted dry is nearly cooked through.

Drain canned tuna thoroughly — press firmly in a Colander or squeeze in a paper towel to remove as much liquid as possible. Excess moisture prevents browning. Mix drained tuna with mayo, lemon juice, salt, pepper, and any mix-ins like celery, pickles, or red onion. If making a sandwich melt, butter one side of each bread slice and set aside. Slice your cheese and have everything ready before the Skillet heats up — cook time moves fast.