To avoid disturbing roots when planting out, sow seeds into large-module trays that provide space for the seedlings to develop. Use peat-based compost.
Make hollows in the compost at the correct depths, and sow seed into them. Cover with compost, water, and cover the trays with clear plastic to keep moist. Keep the trays at the required temperature.
Seeds germinate at different rates, so check often. As soon as seedlings appear, remove any covers, and keep them warm. Thin them as they grow to leave the single strongest plant per module. Harden off and plant out.