Chop 1 of the garlic cloves finely.
In a small bowl, combine honey, paprika, lemon juice, and the minced garlic. Season with ½ teaspoon of salt and a generous amount of black pepper. Add 1 tablespoon of olive oil and mix thoroughly. Rub this mixture all over the steak and let it sit for 15 to 30 minutes.
While the steak marinates, preheat the oven to 350°F. Place walnuts on a rimmed baking sheet and toast them, tossing once, until they turn golden brown, about 8–10 minutes. Once done, transfer the walnuts to a medium bowl. Finely grate the remaining garlic clove over the warm walnuts and mix in 6 tablespoons of olive oil.
When you’re ready to serve, heat a large cast-iron skillet over medium-high heat. Add the remaining 1 tablespoon of olive oil, swirling it to coat the skillet. Place the hanger steak onto the heated surface and cook, turning occasionally, until it is deeply browned and an instant-read thermometer inserted into the thickest part reads 125 to 130°F for medium-rare, approximately 10–12 minutes. After cooking, transfer the steak to a cutting board to rest.
Retain the fat in the skillet and reduce the heat to medium. Arrange the scallions in the skillet in as single a layer as possible, season with salt, and cook, turning occasionally until they are softened and beautifully charred, about 4 minutes. Transfer to a cutting board and chop into bite-sized pieces. Combine the chopped scallions with the walnut mix, vinegar, mustard, and thyme in a bowl, tossing to mix well; season with kosher salt and black pepper.
Slice the steak against the grain and sprinkle with flaky sea salt. Serve it alongside the charred scallion mixture.