Heat oven to 425 degrees. Spray butternut squash squares with olive oil and place on rimmed baking sheet. Roast for 20 minutes. Microwave fennel slices for 2 minutes (you can put them on raw, but I like them softened up a little). On a rimmed baking sheet, combine fennel slices, butternut squash, artichokes, and tomatoes. Spray with olive oil. Season with salt and pepper and stir to evenly coat. Spread in an even layer.
In a small bowl, combine garlic, ground fennel, rosemary, and sage. Season chicken all over with salt and pepper, then rub with spice mixture, putting some under skin of chicken. Nestle chicken among vegetables, skin-side up.
Roast until vegetables are tender and chicken is golden and crisp and cooked through, 35 to 40 minutes.
Plate chicken and vegetables on plater. Scatter olive pieces on top; sprinkle lemon juice and red-pepper flakes on dish. Serve warm.