Place frozen udon noodles into a bowl of cold water and let thaw for 5 minutes. Drain well and set aside.
In a large skillet over medium heat, melt the salted butter and garlic until fragrant.
Add the soy sauce, sesame seeds and chili oil, stirring until the sauce is well combined.
Add the cooked udon noodles to the skillet and toss until they're evenly coated in the spicy garlic butter sauce.
Cook for 1–2 minutes, allowing the noodles to soak up the flavors.
Remove from heat and garnish with chopped green onions and sesame seeds.
Serve immediately and enjoy!