If using sesame seeds: heat a heavy skillet (not nonstick). Toast sesame seeds 2-3 minutes until fragrant, stirring/tossing frequently.
Whisk garlic and sunflower butter together until combined. Beat in oil until combined and smooth. Add remaining ingredients (except spaghetti) and whisk to combine.
Cook pasta according to package directions and drain. Add pasta to “Satay” sauce and stir to coat. Place completed dish in serving bowl, or in individual portions on plates. Top with sesame seeds, if desired.
Ume vinegar is the brine leftover from pickling Japanese umeboshi plums. If substituting for Ume vinegar, replace with 1/4 tsp. kosher salt.
Mirin is Japanese sweet rice wine. If avoiding corn, be sure to find one that does not contain added corn syrup. If substituting for Mirin, replace with 1 1/2 tbsp cider vinegar plus 1/2 tbsp honey or other liquid sweetener.
1/4 cup lemon juice is approximately equal to the juice of two lemons worth. (Strain seeds, of course!)
I used rice spaghetti. Substitute other pastas as appropriate.