Take a few rounds with the Zombies, that should get your heart pumping.
If we get ice-free days here over the winter I can easily get my heart pumping outdoors - I have multiple 10-20% climbs less than 15 minutes from home. The trainer is mainly to keep me busy when the weather is awful.
Also... I think zone 2 makes a lot of sense but I find it hard to stick to on my local rides. Multiple junctions, pedestrian crossings, traffic lights, roadworks and constant changes in gradient! This is an example where I gave up and just rode how I felt like rather than trying to keep to 140-ish W: