Preheat broiler. Melt 4 T. of the butter in a large skillet over medium-high heat. Add the shallot and cook 1 to 2 minutes or until just starting to brown. Sprinkle t he flour over the shallot and butter, and whisk until smooth.
Reduce heat to medium. Add the half-and-half slowly, whisking into a smooth sauce. Cook 2 to 3 minutes, until thickened, whisking as needed. Add the sugar and stir, then add the spinach, nutmeg, salt, and pepper. Cook, stirring occasionally, until hot. Reduce heat to low, so the spinach stays warm.
Place the fillets on a broiler pan that has been coated with cooking spray. Pour the lemon juice over the fillets, then sprinkle the bread crumbs evenly on top. Dot with the remaining butter. Broil 5 to 6 minutes or until the fillets are opaque and the bread crumbs golden.
Spoon some creamed spinach onto each of 4 plates, then place a fillet on top. Serve with the lemon wedges.