1. Preheat oven to 375 degrees Fahrenheit (190 degrees Celsius).
2. In a deep frying pan, heat oil and sauté onions until golden. Add celery and pepper and continue to sauté until vegetables are softened. Add remaining stuffing ingredients and stir until margarine is melted and ingredients meld together.
3. Spray six disposable muffin cups with cooking spray. Slice each salmon fillet lengthwise into three long strips and sprinkle with salt. Working with two strips of salmon per cup, coil fish around the inside edges of the muffin cup, forming a ring with a hole in the center. Build the salmon up the sides of the cups, so that a nice-sized hole remains to stuff.
4. Divide stuffing evenly among cups, filling the cavity and mounding over the top of the fish. Spray tops of cups with cooking spray and bake for 20–22 minutes, until golden. Remove from heat and allow to rest for 10–15 minutes so that the cups don’t fall apart when removing from the pan. Serve warm or cold.