Preheat oven to 255°F (125°C) and line a baking sheet with parchment paper.
Slice the tomatoes into quarters and discard the seeds and pulp. If using long tomatoes, cut each quarter in half again. Transfer the tomatoes to a bowl.
Add the minced garlic, rosemary, oregano, salt, and sugar, and stir to coat. Transfer the tomatoes to the prepared baking sheet and arrange them in an even layer.
Bake for 1 hour and 15 minutes or until semi-dried. You don't want to dry the tomatoes completely, so keep an eye on them. They should have the texture of those sun-dried tomatoes packed in oil. Remove from the oven and set aside.
Guacamole
Add the avocados, diced tomato, minced onion, and garlic to a deep plate or bowl. Mash using a fork until the avocado is almost fully mashed.
Stir in the lime juice, salt, chili powder, and ground black pepper, and stir to combine. Taste and adjust saltiness and sourness if needed.
Transfer to a small serving bowl and top with the dried tomatoes and fresh cilantro. Serve immediately, or refrigerate until chilled for about 2 hours.
Guacamole and dried tomatoes will keep for up to 2 days in the refrigerator. Cover with plastic film to touch to prevent the guacamole from browning.
Notes
Nutritional information will change depending on the size of your avocados.