Combine the radishes, chicken stock, and a generous pinch of salt in a medium pot. Bring to a simmer and cover. Reduce to a simmer and cook until the radishes are tender throughout, about 10 minutes. Uncover and simmer until the broth is reduced to a tablespoon or two.
While radishes braise, prepare the dressing. Combine the cottage cheese, lemon juice, garlic, and zest in a high power blender and blend until completely smooth. Add water as needed to thin the sauce - you want it creamy and coating the back of a spoon well. Season to taste with salt and pepper then stir in parsley. Add to the radishes and toss to coat evenly.
When ready to serve, heat a cast iron pan over high heat as the steak is coming out of the oven. When hot, add the remaining tablespoon of avocado oil. Add the steak to the hot oil (it should sizzle immediately). Cook until steak is golden brown, about 1 minute. Flip and cook the other side the same way.
Remove the steaks and serve with gremolata on top and radishes along side. No need to rest a reverse seared steak.