In a small saucepan, combine peanut butter, coconut milk, red curry paste, and chili peppers. Bring to a low simmer to melt the peanut butter but not a boil, because the coconut milk will separate. Stir until everything is throughly combined.
Remove from heat and add sugar, lemon juice, and salt. Add cilantro at the end and allow sauce to cool. Store in the refrigerator in an airtight container.