Surging Smite (BAX2)

Lightning springs from you to a creature that you try to touch. Make a melee spell attack against the target. On a hit, the target takes 1d6 Lightning damage, and it can’t make Opportunity Attacks until the start of its next turn.

Smite Upgrade. The damage increases by 1d6 when you reach levels 5 (2d6), 11 (3d6), and 17 (4d6).
Using a Higher-Level Spell Slot. The damage increases by 1d6 for each spell slot level above 2.