Pulse about half of the cauliflower in a food processor until the florets break down to fine pieces about the size of rice grains (it's okay if they clump; think of this step as cauliflower "rice" gone wrong). Transfer to a medium saucepan, pulse the remaining cauliflower and add that to the pan too. Add the almond milk, 1 tablespoon of the oil, 1/2 teaspoon salt and several grinds of pepper and bring to a simmer over medium-high heat. Simmer, stirring frequently, until the mixture is soft, smooth and looks like grits, about 10 minutes. Remove from the heat, stir in the nutritional yeast, if using, and adjust the seasoning with more salt and pepper if you'd like. Cover and keep warm.
Heat 1 tablespoon oil in a large skillet over medium-high heat. Add the collards, sprinkle with salt and pepper, and cook, tossing, until slightly wilted and tender, 2 to 3 minutes. Transfer to a bowl and keep warm. Wipe the skillet clean.
Sprinkle the shrimp with salt and pepper. Heat the remaining 2 tablespoons oil over medium-high heat. Add the shrimp, garlic and cayenne, if using. Cook, tossing, until the shrimp are pink and just cooked through, 3 to 4 minutes. Remove from the heat, add the parsley, lemon juice and 1 tablespoon water and stir to coat the shrimp with the sauce.
Divide the cauliflower grits among shallow bowls. Top with the collards and then the shrimp and sauce. Serve with lemon wedges.
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