For tempering, garlic should generally be chopped rather than sliced. Chopping releases more of the garlic's flavor into the oil quickly.
Tempering involves heating spices and aromatics in oil or ghee to infuse the oil with their flavor. When tempering garlic, the goal is to extract its essence rapidly. Chopping garlic increases its surface area, allowing more of its compounds, like allicin (responsible for garlic's pungent flavor), to be released into the hot oil. Slicing, on the other hand, reduces the surface area exposed to the heat, resulting in a milder garlic flavor infusion. The smaller pieces of chopped garlic also brown more quickly, contributing to a richer, more complex flavor profile in the tempered oil. The heat helps to transform the raw garlic flavor into a more mellow and nutty taste.
Be careful not to burn the garlic while tempering. Burnt garlic will impart a bitter taste to your dish. Keep the heat at medium-low and watch the garlic closely, removing the pan from the heat if it starts to brown too quickly.