1. In large saucepot, toast coriander seeds until fragrant (3-5 minutes). Add agave, lemon zest, tarragon, and water; heat to a simmer, stirring to blend. Simmer 10 minutes. Remove from heat; let stand 20 minutes.
2. Add fruit to syrup. Cover pot and return to a low simmer, stirring occasionally. After 10 minutes, begin checking fruit for doneness (tip of sharp knife will slide in easily); transfer to bowl as it is tender. Slip skins from apricots, plums, and peaches; cut all fruit in half. Stir vanilla into syrup. Serve fruit over waffles.