Make salmon the night before so you can use it as leftovers for the sandwich.
Slice cheese, cucumber, onion, tomato and avocado and set aside.
Toast the bread in the toaster oven and on one side place the slice of cheese. If you don't have a toaster oven, you can place the toasted bread in the pan on the stove to melt the cheese.
Heat up the salmon on the stove top in a pan with some olive oil or butter. You can break apart into pieces with spatula. Place the slice of onion in same pan to get a little caramelized.