2 cups canned diced tomatoes
2 T lemon juice
3 garlic cloves, presses
2 -3 t brown sugar
1/2 - 1 t hot chili powder
Bring all of the ingredients to a boil in a small saucepan.  Reduce the heat and simmer uncovered for 30 minutes, or until it thickens a bit.  Allow it to cool, then puree it. If it's too thin for your tastes, you can thin it with a bit of water.
You may also want to add a bit of salt, but I find this depends on which brand of tomatoes I'm using.  Play with the sugar/chili amounts to suit your taste, I like a good spicy-sweet combo.
I'm a condiment junkie, so I usually use this along with a creamy garlic kebab sauce.  Yum!
Have I mentioned how much I love falafel???  Srsly, what an invention!!!