Cut the spaghetti squash in half lengthwise and scoop out the seeds. Brush the halves with olive oil and sprinkle with salt and cayenne pepper. Arrange them on a sheet pan and roast them, flesh side down, until the outside of the squash can be easily pierced with a fork, about 1 hour. Remove from the oven, cover with foil and keep in a warm place.
Add olive oil to a large saute pan until it is about 1/4-inch deep, and put over high heat. While the oil is heating, pat the skate dry with paper towels. Season the fish with salt and the ground coriander seed. When the oil is very hot but not yet smoking, dredge the skate wings in flour and shake of the excess. The fish should go IMMEDIATELY from the flour to the oil, no pausing! If all the fish will not fit in the pan at the same time, only flour the ones that will fit in the pan. Premature flouring will result in a gummy gritty skate wing. The oil should be hot and sizzling when the fish goes in. Cook each piece of fish until golden brown and crispy, about 3 to 4 minutes on each side. Remove from the oil and blot immediately on paper towels. Season with salt, to taste. If working in batches, keep the cooked fish warm in a preheated 225 degree F oven.
While the fish is cooking, coat another large saute pan with olive oil, add the smashed garlic cloves and a pinch of crushed red pepper and put the pan over medium-high heat. When the garlic is golden brown and aromatic, remove it and discard. Add the Brussels sprouts to the pan and season them with salt. Saute the sprouts until they get very brown and crispy.
Using a large fork, scrape the flesh out of the spaghetti squash, it should look like...spaghetti! Add it to the frizzled sprouts and season again with salt. Stir together and toss in the chopped cilantro, reserving a little to garnish the fish.
Arrange some of the squash/and sprout mixture on each serving plate. Lean the crispy skate next to it and sprinkle with the remaining cilantro and a squeeze of lemon juice.