Begin by blanching, peeling, coring, and quartering the tomatoes.
Next, heat a generous amount of olive oil in a large Dutch oven over medium heat.
Once the oil is heated, add minced garlic and dried oregano. Cook until the garlic becomes tender and the oregano becomes fragrant, which should take about two minutes.
Add chopped onion and peppers to the pot, and continue cooking until they are tender, which should take approximately five minutes.
Add the blanched and quartered tomatoes along with sugar to the pot, and let it simmer uncovered for around 45 minutes, or until it reaches the desired consistency. If the tomatoes are watery, you may need to cook the mixture for longer.
Transfer the tomato mixture into hot, sterilized mason jars, making sure to leave enough headspace. Place the jars into a hot water bath and bring the water back to a boil. Boil the jars for approximately 20 minutes longer before removing them from the pot and allowing them to cool.
If any jars do not seal correctly, repeat the hot water bath process with those jars.