Preheat oven to 225°F.
Place tomatoes in a strainer & sprinkle with ½ teaspoon of salt. Let sit for 10 minutes.
Spread tomatoes evenly on parchment lined baking sheet.
Bake tomatoes for 3 hours, then turn oven off & leave tomatoes in the oven for an additional 3 hours to finish the drying process.
To finish the tuna salad, whisk together avocado oil mayo, lemon juice, & Dijon mustard until combined.
Add oven dried tomatoes, remaining ingredients, & dressing to a large bowl. Mix gently until fully combined.