In a large bowl, coat shrimp with sesame oil, garlic, salt, and pepper.
In a separate bowl, dip shrimp into cornstarch, then dust it off vigorously. The cornstarch will taste chalky if there is too much on the shrimp.
In a large skillet, heat oil until it shimmers (but does not smoke) over medium-high heat.
Add corn starch-dusted shrimp. Fry on each side until golden and crisp, roughly 1-2 minutes per side. Remove cooked shrimp and place on a paper towel to remove excess oil.
To make the sauce, pour remaining oil in the pan out into a mug for discarding, and return pan to stove.
Melt butter in the pan over medium-high heat and add garlic and chilies. Heat until garlic is fragrant, 1-2 minutes.
Add chili sauce, sesame seeds, and citrus juice. Heat sauce until bubbling, 2 minutes.
Place shrimp into hot sauce and stir to coat. Add sesame seeds and green onions, then toss to coat.
Serve with rice or plain for a fun appetizer.