Cut potatoes into quarters, chop celery, and finely chop Brussel sprouts
Lightly pan fry your potatoes in 1 Tbsp oil or butter, ΒΌ cup onion, and a pinch of salt/pepper.
Cook until potatoes are slightly tender and onions start to caramelize. About 10 minutes on medium high heat.
Next coat your fillets in the honey mustard dressing and lemon juice then set aside.
Combine the Brussel sprouts, celery, and potatoes/onion together in a casserole pan or sheet pan. Make sure to include all the oil and garlic from the frying pan when you cooked the potatoes.
Mix the vegetables together with a splash of balsamic vinegar and your seasoning (cayenne, paprika, salt, pepper, etc)
Then place your fish fillets on top. Pour extra honey mustard dressing over the entire casserole/pan coating the veggies as well.
Bake at 450 degrees F for 14-17 minutes. Check how the veggies are doing at 14 minutes. If tender then broil the last minute to make Brussel sprouts crispy.
Remove and garnish with parsley or red pepper flakes if desired. Salt and pepper to taste.