Rinse chicken pieces, drain, and put in a large bowl with oil, 1/4 cup lavender blossoms, garlic, and barbecue sauce. Mix well and let stand at least 15 minutes, or cover and chill up to 4 hours.
On a charcoal barbecue: Prepare a solid bed of coals and let burn until medium-hot (you can hold your hand at grill level only 4 to 5 seconds). Dot the surface of coals evenly with 10 charcoal briquets and set grill in place.
On a gas barbecue: Adjust heat to medium (you can hold your hand at grill level only 4 to 5 seconds).
Lay chicken on grill and cover with lid; open vents for charcoal. Cook chicken, turning to brown evenly, until no longer pink at bone in thickest part (cut to test), 25 to 35 minutes. If drippings flare up, move pieces to edge of grill. Transfer to a platter as cooked.
Sprinkle chicken lightly with more lavender blossoms. Add salt to taste. Serve with cucumber salsa.