Probably originally a variant of лууль(luulʹ, “oak-leaved goosefoot”) that got associated with the phrase улаан лооль/лууль(ulaan loolʹ/luulʹ, “tomato”) and later came to mean tomato by itself. If true, the further origin would be Borrowing from Chinese灰綠藜(huīlǜlí, “oak-leaved goosefoot”)