I would never build a veggie garden this way. Burning the sod is fine, if it is legal in your city. The burnt remains may be okay for legume gardens, peas, etc. The better way to good soil base for a veggie garden is to burn out the lawn area with layers of composted material, allowing the topsoil and sod to decompose and add better nutrients to the soil. Even cardboard on the bottom, with compost on top will work.
See here:
http://www.nwedible.com/2012/02/stop-ripping-up-your-lawn-to-grow-veggies.html
Also, if you must have an instant garden, try using one these things. Can be rented for about $10/day and is dead easy to use. No grunting or sweating at all. Tilling or weaseling will leave a lot of root matter and depending on time of year, seed: