Shop for a combination, not a script
I look for two vegetables that roast well, a leafy ingredient and something acidic for the dressing. The exact selection changes with the market and the budget. The point is to have contrasting textures rather than reproduce a photograph using ingredients that are expensive or difficult to find.
Give the oven one clear job
Cut firm vegetables into similar pieces, dry them and leave space on the tray. Crowding makes them steam. Turn the tray when necessary and check the pieces rather than relying only on a timer. Different ovens, vegetables and cuts need different amounts of time to develop a browned edge.
Build the rest while it cooks
A pot of barley, rice or lentils gives the meal substance. Follow the packet instructions and season after tasting. Wash the greens, mix lemon juice or vinegar with oil and prepare a handful of seeds. None of these steps needs a specialised appliance or a complicated sauce.