Fill a large bowl with ice water. Peel and rinse the potatoes. Cut each potato into 4 or 5 slices lengthwise, then cut each piece into fries. Place the fries in the ice water.
Halve the avocados and remove the pits. Dice the avocados in their shells, then squeeze the flesh into a medium bowl. Mash the avocados with the back of a fork until you reach the desired consistency for guacamole. Fold in the lime juice, Roma tomato and jalapeño. Season with salt and pepper and set aside.
Heat a large cast-iron skillet over medium-high heat; line a plate with paper towels. Add the chorizo to the skillet and cook until browned, 5 to 8 minutes, then transfer to the lined plate to drain. Lightly clean the skillet and lower the heat to medium low. Add the cheese and fire-roasted tomatoes and green chiles. Cook, stirring frequently, until the cheese has melted. Fold in the chorizo and place on a very low burner until ready to use.
Fill a large, heavy-bottomed pot with a few inches of oil. Heat the oil to 300 degrees F.
Drain and rinse the potatoes under cold water for 15 to 20 seconds. Transfer to a baking sheet lined with paper towels and blot with the paper towels to dry them. Line a second baking sheet with fresh paper towels.
Fry the potatoes in 2 batches until they are slightly softened but have no color, 3 to 4 minutes. Remove to the fresh paper towels to drain
Heat the oil to 400 degrees F; line a third baking sheet with fresh paper towels. Fry the potatoes in 2 batches until golden and crisp, 2 to 3 minutes. Drain on the paper towels.
Sprinkle the seasoning salt over the fries, then toss and place on a platter.
Top the fries with half of the queso con chorizo followed by the guacamole, sour cream, cilantro and pimentos. Transfer the remaining queso con chorizo to a serving bowl and serve alongside the fries.