I would do what Jodi suggested. My DD has recently started to learn "Hot" and "Cold" and the only way she has learnt was from experiencing both.
Before I used to say "Darling, please don't touch that, its hot" and she wouldn't understand, but now that I let her touch a hot cup of coffee and I tell her the same thing, she tells me "Hot" and leaves it alone.
I never really had a issue with the oven, in my old house the oven was on the floor, and I was lucky coz DD never seemed interested in the oven. Now she understands hot, so she doesn't even attempt it.

More drastically, you could gate off the kitchen (if possible) so he is unable to get into there unattended.