Letter of recommendation from a senior lecturer
A clarification for what you need a letter would help. But, any letter that highlight academic skills should be useful. It will show your capacity to plan and carry out work so regardless of whether it is research or teaching you should get a leter. And, in each case the person most qualified to provide the letter should write it. 

Providing letters that describe traits that are not sought after in an application will of course not be optimal (probably not detreimental, however). You therefore need to chose your authors of letters to match the skills requested for your application purpose.