Begin by bringing a large pot of water to a boil. Add the buckwheat soba noodles and cook according to the package instructions, usually around 4-6 minutes. Be careful not to overcook them; you want them to be al dente. Drain the noodles and rinse them under cold water to stop the cooking process. Set aside.
In a small bowl, whisk together the almond butter, water, rice vinegar, soy sauce, and crushed red pepper flakes (if using). Adjust the consistency with more water if you prefer a thinner sauce. Set aside.
In a large skillet or wok, heat a drizzle of extra-virgin olive oil over medium-high heat. Add the minced garlic and ginger, stirring quickly for about 30 seconds until fragrant.
Toss in the red bell pepper, shredded cabbage, and broccoli florets. Stir-fry for about 5-7 minutes until the vegetables are tender yet still crisp.
Add the cooked soba noodles to the skillet with the vegetables. Pour the almond butter sauce over the top and toss everything together until well combined and heated through, about 2-3 minutes.
Remove from heat and sprinkle with sliced scallions and almond slivers for added crunch. Serve hot, with extra crushed red pepper flakes on the side for those who like it spicy!