1. Heat your grill to high. Devein and deseed your red peppers, and cut them into quarters. Lightly coat them in olive oil and grill them, outside first, until they are lightly charred. Remove and let cool. Do not remove the skins, the charred bits add flavor and color to the sauce.
2. While you are grilling, add a half tablespoon of olive oil to a large pan, preferably a straight-sided 4 Qt. saute pan with a lid, and cook the onions until they are soft but not browning. Then add your half a can of San Marzano tomatoes: I usually scoop them out of the can into the pan, and then quickly, but very carefully and slowly pick each one up and crush it in my fist. You have to be careful because they'll squirt juice! Another option is to slice them with a knife in the pan, and then carefully break them apart with a spoon; or just crush them ahead of time into a separate bowl. Cook them on low, partially covered, slowly bringing them up to a simmer.
3. Then, in a food processor, combine your prepared peppers, 1/2 cup of vegetarian chicken broth, 1 tbsp balsamic vinegar, and 1 tbsp extra virgin olive oil until it has the consistence of a sauce. Add the mixture to your already cooking tomatoes, bring to a simmer, and then continue over medium-low heat, uncovered, for about 15 minutes until some of the water is evaporated off and it's more sauce-like. You may want to add salt and pepper at this point but I've found that it normally doesn't need it.
4. NOTE: Using the finest ingredients is important. Quality olive oil costs more but has a much better flavor, as do the San Marzano tomatoes. I use the Cento or Rosa brand which come in 28 oz. cans. The remainder can be frozen if needed. For the chicken broth I use the Harvest2000 brand ( ) which is completely vegetarian and utilizes no MSG. I mix it to double strength or more, at least 2 tsps. per half cup of water.