Halibut is a light but flavorful fish; combining it with an herby chimichurri and an acidic tomato salad helps highlight the flavors. Chimichurri is a garlic and parsley based sauce and is very popular in many South American countries. Most chimichurri is pretty oily but I halved the olive oil in this recipe, if you prefer a more traditional style you can increase it to a full cup.
Preheat a water bath to 130°F (54.4°C).
Mix the spices together in a bowl. Salt and pepper the halibut then sprinkle with the spice mixture. Place in the sous vide bag with the olive oil and lightly seal. Let the fish sit for 30 minutes for the dry brine to take effect then place in the water bath and cook for 15 to 45 minutes, until heated through.
Combine all the ingredients in a blender or food processor and process until combined well.
Combine the garlic and vinegar in a bowl and let sit for 5 minutes. Add the olive oil and whisk to combine. Toss the remaining ingredients with the dressing.
Take the halibut out of the bag and dry it thoroughly using paper towels or a dish cloth. Sear one side over high heat just until browned, 1 to 2 minutes. Remove from the heat.
Place some of the tomato and onion salad on a plate and top with the halibut. Drizzle some chimichurri sauce on the top then sprinkle with parsley and serve.