Make the chicken-fried mushrooms: Trim any tough woody ends from oyster mushrooms, making sure to keep root intact. Slice bunches lengthwise through the root into 1/2-inch thick planks. Keep any pieces of mushroom that fall off of planks to batter separately.
In a shallow bowl, whisk together flour, cornstarch, paprika, garlic powder, onion powder, turmeric, ¾ teaspoon salt, and ¼ teaspoon pepper. In another shallow bowl, whisk together almond milk and vinegar.
Working with one at a time, toss mushroom steaks into flour mixture, making sure to coat the nooks and crannies. Dip in almond milk. Repeat, tossing in flour, dipping in almond milk, and tossing again in flour and transfer to a plate. Repeat with remaining mushrooms, arranging them in a single layer on plate. Repeat with any extra mushroom bits.
Pour oil into a large cast-iron skillet until it comes ½ inch up side of skillet and place over medium-high heat. When oil is hot and just starts to shimmer, reduce heat to medium. Fry mushrooms in 2 batches, turning once, until golden brown on both sides, about 8 minutes per side for large planks and 4 minutes per side for smaller planks and mushroom bits. Transfer to a paper towel–lined plate to drain and sprinkle with sea salt.
Meanwhile, make gravy: In a small saucepan, melt butter over medium-high heat. Add cremini mushrooms and cook, stirring occasionally, until golden, about 3 minutes. Add garlic and cook, stirring until fragrant, 1 minute.
Add flour to mushroom mixture and cook, stirring, 1 minute. Whisking constantly, slowly pour almond milk into mushroom mixture. Bring to a boil, reduce heat to medium and simmer, stirring often, until gravy thickens, about 10 minutes. Season to taste with salt and pepper.
Serve mushrooms topped with gravy, chives, and more pepper.