Mix all the ingredients for marinade together in a bowl. Whisk until sugar dissolves.
Toss shrimp in marinade, cover, and let it sit at room temperature for 30 minutes.
When ready to cook, remove shrimp from marinade; transfer the marinade to a small saucepan. Bring to a simmer, cooking gently for at least 5 minutes then taste and adjust seasonings as desired.
Heat avocado oil in a skillet over medium-high heat. Brown the shrimp on one side before flipping to cook completely on the other side.
When fully cooked, transfer shrimp to a serving dish; garnish with sesame seeds, scallions, and/or cilantro. Serve alongside cooked marinade.