In a food processor, mix sundried tomatoes, pistachios, roasted garlic, red pepper flakes, and salt. Once a thick paste is formed and the mixture starts to ball up, slowly drizzle the olive oil from the jar into the spout opening of the food processor’s top until the pesto reaches a smooth glossy texture. If the mixture needs more oil, add fresh olive oil a tiny bit at a time. Taste and add salt if needed.