Slice off the stems of the Brussels sprouts & cut in half lengthwise. Toss with olive oil, salt, pepper & red pepper flakes. Spread on a lined baking sheet, cut side down to allow for browning.
Bake 25-30 minutes until browned and crisp, pausing after 15 minutes to turn.
Meanwhile, combine all ingredients for the avocado dressing in the blender and blend until smooth, scraping down the sides as necessary. Add additional water, salt, and pepper to taste.
Serve the Brussels sprouts hot out of the oven alongside lemon wedges for squeezing over the sprouts and the avocado dressing.