Preheat the oven to broil.
Line a large baking sheet with parchment paper.
Slice the tomatoes in half and remove cores. Set skin side up on the baking sheet.
Remove stems from the jalapeño peppers and habanero peppers. Cut in half lengthwise. Set on the baking sheet, skin side up.
Cut onion half in half. Place on the baking sheet.
Brush vegetables with oil.
Set rack in the top ⅓ of the oven and broil for 15 minutes. Keep an eye on them. Do not leave unattended.
Turn off the oven and set the pan aside to cool.
Once ingredients have cooled some, put them into your food processor with the cilantro, garlic and salt. Process until the consistency you want.
Add the diced mangoes and pulse the food processor until the mangoes are mixed with the rest of the salsa.
Transfer to a bowl and cover. Refrigerate for about 4 hours for flavors to blend.