Heat oven to 375 degrees. Have 2 large rimmed baking sheets ready.
Remove core and outer leaves from cauliflower heads. Break florets apart, then cut them into large, nearly bite-size, pieces. Place in a large bowl. Add oil; toss to coat well.
Divide cauliflower among baking sheets, spreading them in a single layer. Sprinkle generously with the everything bagel seasoning blend and the salt.
Roast, stirring once or twice, until tender when pierced with a knife and slightly golden, about 20 minutes. If working ahead, cool completely before packing into covered containers. Reheat in the microwave and garnish with parsley.