Yellow could be due to a shortage of nitrogen. Lettuce likes to have some nitrogen to grow a lot of green leaves. Peas can fix their own out of the air, so that would explain why they're doing OK. Try hitting it with some soluble fertilizer, if you use the stuff.

As far as the holes, they could be due to slugs or sow bugs. I've noticed around here (Missouri, admittedly a long way from you) that mulches are havens for these buggers and they can munch leaves in nothing flat when there are a lot of them. I tend to grow my spring lettuce close together in bare soil so I haven't had them attack it. Not sure what you'd do, since if you spray anything on it you're going to be eating it very soon. Maybe someone has an organic recommendation. Insecticidal soap, maybe.

we use lasagne raised beds and have none of those problems our lettuce grows as volunteers, we use hay type mulches to keep the gardens mulched and all our rottable kitchen scraps get tucked under the mulch just about daily so we are continualy feeding the medium which started as mushroom compost from the farm.

our vege's are generally watered with dish water some laundry water and my pee added to pre-rinse dish water, and when not enough of the above rain water.

len

Here is a link that might be useful: lens garden page

What kind of "bugs". There are good bugs, beneficials, innocuous bugs, ones that are there that seem to be around only as a food source for others, and there are the bad bugs, the ones that eat our plants, or sting us. Contrary to what some might think the "bugs" that help digest organic matter, ants, pill bugs, millipedes, earwigs, and many others are not bad and are in fact beneficial since they help clean up our planet.
Yellowing plant leaves can indicate many problems, not just a Nitrogen deficiency. Yellowing of leaves also can indicate deficiencies of Potassium, Zinc, Iron, Sulfur, Boron, Copper, Manganese, or Molybdenum, or may indicate the soil is too cold and the soil bacteria are not yet active enough to provide the nutrients the plants need to grow, or maybe there is not enough soil moisture and the plants cannot uptake those soil nutrients, or maybe the soil is too wet and there is too little air the plants roots also need to be able to uptake those soil nutrients.

Occam's Razor suggests it's the most common deficiency. While everything you're saying is correct, I doubt a healthy compost pile has a molybdenum problem.