and if you *do* step in front of the truck your change in kinetic energy in the frame of reference of the ground will be identical to your change in kinetic energy relative to the frame of reference of the truck.
But will it?
Say you are walking towards the truck at 5 Km/Hr relative to the ground then stop. Your change in KE relative to the ground is 0.5*m*V^2 say 25 units.
Relative to the frame of reference of the truck moving uniformly at say 50 Km/Hr over the ground towards you, it observed you had a relative velocity of 55 Km/Hr initially, then 50 Km/Hr after you had stopped walking towards the truck.
Change in KE according to the truck’s frame of reference = (55*55) - (50*50) = 3025 - 2500 = 525 units.