Preheat barbecue to medium.
1. Remove husks from corn cobs. Brush 1 tbsp (15 mL) olive oil on all sides and place on preheated grill. Brush tomatoes and chiles with remaining oil and place on grill. Grill, turning to brown all sides, about 20 minutes. When the corn starts to brown, remove from heat and let cool. When chiles and tomatoes start to blister, place in a plastic bag to sweat for 20 minutes.
2. Slice corn from cobs and place in a large bowl. Peel skins from sweated chiles. Cut chiles in half and scrape out seeds and membranes.
3. In work bowl fitted with metal blade, pulse chiles until chunky, about 10 times. Add to corn.
4. Peel skins off sweated tomatoes, remove cores and cut in half. Try removing all of the seeds. Place in same work bowl fitted with metal blade and pulse until smooth, about 10 times. Add to corn mixture.
5. In same work bowl fitted with metal blade, pulse onion, vinegar, sugar, oregano and salt until chunky, about 10 times. Add to corn mixture. Stir to combine. Let rest for 30 minutes.
You can use cherry tomatoes in place of Roma and you won’t have to seed them.
Use a combination of 6 oz (175 g) jalapeño or hot banana peppers and 6 oz (175 g) poblano or cubanelle peppers if you can’t find New Mexico chiles.