Heat your oven to 300˚F. Spread the pistachios on a sheet tray. Roast until fragrant and starting to brown, 15 minutes. Remove, let cool, and chop into mostly fine pieces.
While the pistachios are roasting, trim the end from the scallion and thinly slice (slicing back and forth across the scallion, not chopping). Place the scallions in a strainer and rinse with cold water. Drain and pat dry the scallions dry in a clean cloth. Let air dry until ready to use (see note).
Core the tomatoes and cut into wedges. Place in a bowl and sprinkle with the salt, jalapenos, 2/3rds of the chopped pistachios, and 2/3rds of the sliced scallions. Toss until combined and transfer to a serving bowl with any pistachios/scallions left in the bowl. Leave as much tomato liquid behind as possible.
Heat the olive oil in a small pot over medium-low heat. When hot, add in the cracked cumin and sizzle for about 20 seconds- just until fragrant/slightly darken in color. Remove from heat and spoon over the tomato mixture, trying to distribute as best as possible evenly. Finish with the remaining scallions and pistachios before serving.