Set the fillets in a baking dish with side that did not originally have skin, facing up.
Mix together the shallot, dill, mustard, lemon juice, canola oil, red pepper flakes, and pepper in a bowl. Smear the mixture over the fillets. Bake for about 8 to 10 minutes.
Steam the cabbage for 7 to 10 minutes or until the cabbage is crisp.
Mix together the margarine, lemon juice, salt, and pepper in a measuring glass. Microwave for 25 to 30 seconds on high to melt. Put the cabbage in a bowl and drizzle the margarine mixture over the cabbage.
Separate the cabbage onto 2 plates and place the fillets on top.