Place the grouper and shrimp in a large bowl. Toss with the lime and orange juice and let stand for 30 minutes. Strain the grouper and shrimp and place in a separate bowl.
Add the Cold-Smoked Grape Tomatoes, cilantro, onions, chiles, mango, salt and pepper and toss gently to combine. Drizzle with the olive oil and toss.
Place the ceviche on a serving platter or on individual plates. Drizzle with a bit more olive oil. Garnish with Pickled Red Onions, lime zest and plantain chips.
Cold-Smoked Grape Tomatoes:
Put a handful of hot coals in the bottom of a smoker. Scatter the hickory chips over the top. Put a try of ice on the bottom grate. Put the cooking grate above the ice tray. When the temperature of the smoker reaches 100 degrees F, toss the tomatoes with the canola oil and sprinkle with salt and pepper. Place the tomatoes on the top grate. Close the smoker and smoke the tomatoes for 10 to 20 minutes, depending on how smoky you want them.
Pickled Red Onions:
Bring the vinegar, sugar, mustard seeds and 1 tablespoon salt to a boil in a small saucepan and cook until the sugar and salt dissolves, about 1 minute. Transfer to a small bowl and let cool for 10 minutes. Add the onions and stir to combine. Cover and refrigerate for at least 1 hour and up to 24 hours.