Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper or foil.
In a small bowl, stir together the olive oil, coriander, cumin and salt. Rub the skinless surface of the salmon with the olive oil mixture.
Bake the salmon until just cooked through, taking care not to overcook. Depending on the thickness of the salmon fillet, this will take anywhere from 7 to 10 minutes. Squeeze the lime over the salmon. Use a fork to break it into chunks.
Spread 2 tablespoons guacamole on each tostada. Divide the salmon, shredded cabbage mix, salsa verde and cilantro. Serve.
Scoop out the avocado into a bowl. Use the back of a fork to smash the avocado until fairly smooth. Stir in the lime juice, salt and diced tomato.