I live in a hilly area and do a ton of zone 2. My key is east gearing, ideally with gravel bike gearing. For example, I use a 40t front ring and 10-44 cassette. My zone 2 uphill is almost always in the 44 cog riding 4-6 mph depending on the grade.

My road bike as 36 front and 34 rear and it’s really hard to do zone 2 in hills for me.