Pre-heat your oven to 400°F
Place the whole tomatoes in a mixing bowl and add 2 tsp of the olive oil, ¾ tsp of the sea salt and a ½ tsp of the freshly ground pepper. Toss the tomatoes before slicing them in half and spreading them out on a baking tray cut side up.
Cut the zucchinis lengthwise and then into ¼" slices. Place them in the mixing bowl used for the tomatoes and add 1 tsp of the olive oil, ½ tsp of the sea salt and ¼ tsp of the freshly ground pepper. Toss and spread out over part of a second baking sheet.
Cut the onions into ¼″ slices and place these on the baking sheet with the zucchinis. drizzle with ½ tsp of olive oil and salt and pepper to taste.
Peel the squash and cut into ½″ cubes so that all of the veg can be roast slowly and be ready at the same time. Place them in the mixing bowl used for the other vegetables and add 1 tsp of the olive oil, ½ tsp of the sea salt and ¼ tsp of the freshly ground pepper. Toss and spread out over a third baking sheet.
Peel the loose outer skins from the garlic bulbs, leaving the inner peel on the individual cloves intact. Slice the top of the bulb off to expose the cloves and brush the tops of the cloves lightly with the remaining ½ tsp of olive, before setting them on one of the three baking sheets.
Roast vegetables for 40 minutes at 400°F, turning once half way through. Roasting is complete when squash is fork tender. Combine all roasted veg with the exception of the garlic, in a covered dish to keep warm.